1. Field of the Invention
The present invention relates to a cart braking device, and in particular to a cart braking device has functions of wheel braking and directional locking.
2. The Prior Arts
A cart is used to carry merchandise, goods, luggage, etc. to provide laborsaving and convenient transportation. In order to prevent the cart from rolling when unattended by the user, a cart braking device is developed to eliminate the hazard caused by free-wheeling cart.
A conventional cart braking device has various types, such as a handle type handbrake, a pedal type footbrake, etc. The conventional cart braking device usually uses a brake pad to directly press against a tread surface of a wheel, thereby stopping the movement thereof.
Referring to FIGS. 1-3, a conventional cart braking device includes a central shaft 100, an orientation piece 101, a braking pad 103, a screw 104, and an fixation piece 105. The screw 104 connects the braking pad 103 to a lower end of the shaft 100. The orientation piece 101 having a plurality of teeth 102 is mounted on the shaft 100. The elastic fixation piece 105 is disposed by the central shaft 100 and is provided with at least one projected arm 106. A spring 108 is sleeved on the central shaft 100 and a cap 109 is mounted on a top of the central shaft 100. Referring to FIG. 3, when the central shaft 100 is pushed downward, the braking pad 103 is moved downward and pressed against a tread surface of a caster wheel 107. Thus, the wheel 107 is fixed and kept stationary. Moreover, the teeth 102 of the orientation piece 101 are engaged with the projected arms 106, so the central shaft 100 can not be rotated and the wheel 107 can not be rotated about the central shaft 100, thereby locking the direction of the wheel. Therefore, the cart braking device has functions of wheel braking and directional locking. Referring to FIG. 2, the compressed spring 108 returns to its original state after the pressing force is released from the central shaft 100. Elastic force of the spring 108 is applied on the cap 109, and therefore the central shaft 100 is moved upward with the cap 109. The braking pad 103 is moved upward with the central shaft 100 and is separated from the wheel 107. A distance is kept between the braking pad 103 and the tire surface of the wheel 107. The orientation piece 101 is disengaged from the fixation piece 105. Thus the wheel 107 can freely be rotated about an axis of the wheel 107 and about the central shaft 100.
Although the conventional cart braking device has the functions of wheel braking and directional locking, it still has the following disadvantages.
(1) The braking pad 103 is pressed against the tread surface of the wheel 107. After a period of time, the tread surface worn out. The braking pad 103 can no longer fully contact with the tread surface of the wheel 107, so the braking is not functioning well. Then, it needs to replaces the wheel 107.
(2) When the cart moves, the tread surface is contacted with the floor at a circumferential center line of the wheel 107. The braking pad 103 is directly pressed on the circumferential center line of the wheel 107. Repeated use of the cart braking device wears the wheel 107 and causes uneven wear on the tread surface at the circumferential center line of the wheel 107. The uneven tread surface results in cart bumping on the floor and collision of objects in the cart, when the cart moves. The disadvantage is serious, especially when the cart is used to transport very ill patient or precision instruments. It makes the patient uncomfortable and damages the precision instruments.
(3) When the projected arms 106 of the fixation piece 105 are engaged with the teeth 102 of orientation piece 101, end portions of the teeth 102 are in contact with sides of the projected arms 106. The end portions of the teeth 102 of the orientation piece 101 are rectangular and a pitch of the teeth 102 is large. Although elasticity of the orientation piece 101 can help the projected arms 106 to be engaged with the teeth 102, it has to rotate the orientation piece 101 at certain angles to engage the teeth 102 with the projected arms 106. Thus, the engagement of the teeth 102 and the projected arms 106 is intermittent but not continuous.